1. Field of the Invention
The invention relates to an actuating device for an on/off valve having a pneumatic drive which is connected to a compressed air supply by a solenoid valve, wherein the solenoid valve ventilates the pneumatic drive with the compressed air when driven with a control voltage and vents the pneumatic drive when the control voltage is not present, and the pneumatic drive moves the valve into an operating position during ventilation and moves the valve into a safety position during venting, and a means for performing a partial stroke test.
2. Description of the Related Art
In a known actuating device disclosed in DE 10 2006 003 750 A1 or DE 10 2005 004 477 A1, a pneumatic on/off valve, in particular an emergency shut-down (ESD) valve, is moved by a pneumatic drive either into an operating position, for example “on”, or into a safety position, for example “off”. A solenoid valve which is driven with a control voltage provided by a control system connects the pneumatic drive to a compressed air supply. In an emergency, the control voltage is switched off to vent the pneumatic drive with the solenoid valve. As a result, the valve is moved from the operating position into the safety position.
In order to allow the functionality of the actuating device to be checked as part of a partial stroke test, an additional position regulator is fitted to the pneumatic drive. During the partial stroke test, the valve is moved by the position regulator from the operating position over a portion of its actuating travel, and is then moved back again. In this case, the change in position is so small that there is no need to interrupt ongoing operation of the installation in which the actuating valve is installed, and its operation is disrupted only to an insignificant extent. During the partial stroke test, the actuating movement is recorded and stored. In order to drive the position regulator, an analog output subassembly must be provided in the control system, which subassembly provides a 4-20 mA signal, for example, in order to transmit the desired value for the valve controller. If the test is not evaluated in the position regulator itself, an analog input subassembly, to which the position regulator transmits the position data recorded by it, must also be provided in the control system.
Providing a position regulator only for the partial stroke test involves a large amount of material and financial expenditure. In addition, although the fitting comprising the valve and pneumatic drive can be tested using the position regulator and the partial stroke test carried out by the latter, the solenoid valve cannot be tested in this manner and requires a further test method.